Catalytic activated carbon for removal of chloramines from water

ABSTRACT

This application discloses a method for enhanced removal of chloramines from a chloramines-containing fluid media by contacting said media with a catalytic activated carbon characterized by having present in the graphene structure of the carbon from 0.01 to 10 wt % of aromatic nitrogen species. The catalytic activated carbons used in the present invention may be prepared from carbon materials that have been contacted or otherwise exposed to ammonia, with or without simultaneous exposure to an oxygen-containing vapor or gas at temperatures above 700° C. and, preferably, are in the form of a solid carbon block.

[0001] This application is a continuation-in-part application ofcommonly assigned and co-pending Ser. No. 10/144,201, titled “ImprovedMethod for Removal of Chloramines From Drinking Water,” by Frederick S.Baker and Jane F. Byrne, filed on May 10, 2002, which application is acontinuation-in-part of commonly assigned and co-pending Ser. No.10/141,158, titled “Improved Method for Removal of Chloramines FromDrinking Water,” by Frederick S. Baker and Jane F. Byrne, filed on May8, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to improvements in the use of ahigh-performance, catalytically activated carbon for the removal ofchloramines from chloramine-containing fluid streams. In particular,this application relates to the use of high-performance, catalyticallyactivated carbon filters for the removal of chloramines fromchloramine-containing fluid streams wherein the carbon characterized byhaving present in the graphene structure of the carbon from 0.01 to 10wt % of aromatic nitrogen species.

[0004] 2. Description of the Prior Art

[0005] While chlorination has made the U.S. water supply safe fromillness producing bacteria, viruses, and parasites, an unhealthyby-product of chlorinating water that contains natural organics is theproduction of trihalomethanes, which have been linked to increased riskof cancer. One way to reduce this risk is to change from chlorinedisinfection to chloramine disinfection. Chloramines are formed from thereaction between ammonia and chlorine. Thus, adding ammonia (NH3) to achlorination system converts chlorine to chloramines. Specifically,monochloramine, hereafter referred to as “chloramine,” in lowconcentrations arise from the disinfection of potable water sources. Toimprove the taste and odor of the water and to remove the inherentlytoxic chloramine, the water is typically contacted with activatedcarbon. The ability of carbonaceous materials, such as activated carbon,to remove chloramine from aqueous streams is generally well known. It isalso known that improvements in removal of chloramine can be achieved byreducing the mean particle diameter of the carbon and by increasing thecarbon bed contact time. In some applications, such as in kidneydialysis units, high removal rates of chloramine are particularlyimportant. Although parameters such as contact time and mean particlediameter are known to affect chloramine removal efficiencies, removalperformance is neither well understood nor particularly effective.

[0006] Activated carbon is used in the treatment of water in the form ofpowdered activated carbon, granular activated carbon, or shapedactivated carbon, such as pellets or spheres. Another form of shapedactivated carbon often recommended for point-of-use (POU) andpoint-of-entry (POE) water treatment, however, is solid block activatedcarbon. Block activated carbon is a compressed blend of selectedactivated carbon and a binder material, such as high densitypolyethylene (HDPE), which is capable of adsorbing a wide range oforganic materials. Water is forced through the pores of the denselycompacted carbon block, where a combination of mechanical filtration,electrokinetic adsorption, and physicauchemical adsorption takes placeto reduce or eliminate a wide range of contaminants.

[0007] U.S. Pat. No. 5,338,458, issued on Aug. 16, 1994 to Carrubba etal., titled “Method for Removing Chloramine with Catalytic Carbon,”teaches an improved process for the removal of chloramine from gas orliquid media by contacting said media with a catalytically-activecarbonaceous char. In practice, however, a product manufacturedaccording to the patent teaching has been found lacking in effectivenessfor chloramine removal from drinking water. Additionally, attempts toreplicate even the relatively poor performance of the commercial productbased on the '458 patent (Centaur®) in solid block form has not beensatisfactory. Apparently, the impact of the binder component detractsmeasurably from the prior art carbon's performance for chloramineremoval.

[0008] The applicants' pending application Ser. No. 10/141,158, filedMay 8, 2002 teaches an improved method of removal of chloramine fromdrinking water with an activated carbon that is made catalyticallyactive for removal of chloramines by a process of pyrolyzing the(primarily wood-based) carbon while simultaneously passing a gas streamcomprised of a mixture of NH₃ and an oxygen-containing gas through thecarbon.

[0009] Also, the applicants' pending application Ser. No. 10/144,201,filed May 10, 2002 teaches an improved method of removal of chloraminefrom drinking water with an activated carbon that is made catalyticallyactive for removal of chloramines by a process of pyrolyzing the(primarily wood-based) carbon while simultaneously passing a gas streamcomprised of a mixture of NH₃ and an oxygen-containing gas through thecarbon, wherein the activated carbon is in the form of a solid block.

[0010] While the inventions of these prior applications showed greatimprovement in chloramine removal efficiency over the prior art Centaur®catalytic activated (primarily coal-based) carbons of U.S. Pat. No.5,338,458, a complete understanding of the reasons for such benefitswere not entirely understood. Moreover, it was appreciated that havingsuch understanding could permit controlling the process for treating theactivated carbon in a manner to achieve further improved chloramineremoval efficiencies and enhanced process productivity.

[0011] Accordingly, it is the object of the present invention to providegreater improvements in removal of chloramines from drinking water. Itis a further object of the invention to provide an activated carbon thatis catalytically active for removal of chloramines apart from factorssuch as extended contact time, mean particle diameter, and the likewhich factors are known to affect removal of chloramines. Finally, it isan object of this invention to provide an improved method of chloraminesremoval using an activated carbon that is catalytically active forremoval of chloramines in the form of a solid block activated carbon.

SUMMARY OF THE INVENTION

[0012] Generally, the present invention comprises a method for enhancedremoval of chloramine from aqueous media by contacting said media with acatalytic activated carbon. The catalytic activated carbons used in thepresent invention may be prepared from carbon materials that have beencontacted or otherwise exposed to nitrogen-containing compounds attemperatures above 700° C. In particular, the catalytic activatedcarbons used in the present invention may be contacted or otherwiseexposed to ammonia, in or out of the presence of an oxygen-containinggas or vapor, at temperatures above 700° C.

[0013] The carbonaceous feedstocks from which such carbons are producedare relatively nitrogen-poor, naturally occurring materials, such aslignocellulosic materials and coals. The lignocellulosic materials mayinclude carbons derived from wood, olive pits, and various nut shells,including coconut. The nitrogen-poor feedstocks may be processed aslow-temperature carbonized chars or as high-temperature carbonized charssuch as activated carbons. Either processed carbon may be oxidized priorto, during, or after carbonization. However, all nitrogen-poor charsmust be contacted or otherwise exposed to nitrogen-containing compoundssuch as ammonia, at high temperatures prior to, during, or aftercalcination and/or activation at high temperatures. The contact with anitrogen-containing compound at high temperatures may be in or out ofthe presence of a gasifying agent, such as steam or carbon dioxide.Additionally, it is essential that the final products in all casesdescribed above be cooled to temperatures below 400° C., preferably 200°C., in an oxygen-free or otherwise inert atmosphere.

[0014] The catalytic activated carbons of the present invention aredistinguished from prior art carbons by their ability to extract agreater amount chloramine from chloramine-contaminated drinking watermore rapidly. When tested under nearly equivalent conditions of contacttime, niean particle diameter, concentration of chloramine, and thelike, these catalytic activated carbons remove chloramine much moreeffectively than prior art carbon materials, which have been used forthis application in the past, including the carbonaceous chars of U.S.Pat. No. 5,338,458. Other advantages of the present invention willbecome apparent from a perusal of the detailed description of thepresently preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a graphical representation of chloramine-reductionperformance of invention carbon products and prior art carbon product ona gravimetric basis.

[0016]FIG. 2 is a graphical representation of chloramine-reductionperformance of invention carbon products and prior art carbon product ona volumetric basis.

[0017]FIG. 3 is a graphical representation of hydrogen peroxide (H₂O₂)decomposition rates for invention carbon products and prior art carbonproduct.

[0018]FIG. 4 is a graphical representation of the lack of thecorrelation between the chloramine-reduction performance and the “t-¾time” of catalytic carbon products.

[0019]FIG. 5 is a graphical representation of the correlation betweenthe chloramine-reduction performance and the nitrogen content ofcatalytic carbon products.

[0020]FIG. 6 is a graphical representation of the graphene structure ina catalytic activated carbon showing the different nitrogen speciesidentified by XPS analysis as being present in either the catalyticcarbon of the subject invention and/or the product of the '458 patentprior art process.

[0021]FIG. 7 is a graphical representation of the enhancement of thechloramine reduction performance of the prior art Centaur productthrough application of the invention process.

[0022]FIG. 8 is a graphical representation of the enhancement ofchloramine reduction performance obtained at relatively low temperatureby treating a carbon with ammonia in the absence of an oxygen-containinggas.

[0023]FIG. 9 is a graphical representation of the influence ofpolyethylene binder on the chloramine-reduction performance of inventioncarbon product and prior art carbon product.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0024] As noted above, potential toxicity, unpleasant taste, and odorare associated with the use of chloramine disinfection by potablewater-treatment plants. Also, as noted, the prior art teaches thateffective removal of chloramine from water requires acatalytically-active carbonaceous char, which has been characterized asa carbon that will rapidly decompose hydrogen peroxide in aqueoussolution. It is the object of this invention, more specifically, toprovide a catalytic activated carbon that exhibits high performance forchloramine removal from water, yet possesses relatively low activity forhydrogen peroxide decomposition compared to prior art carbons. It is afurther objective to demonstrate that the invention process for removalof chloramine employing said catalytic activated carbon is an unexpectedand surprising (in light of the prior art teaching) improvement overprior art process performance in removing chloramine employing prior artcarbons.

[0025] While it is appreciated that the U.S. Pat. No. 5,338,458patentees disclose “activated carbon” as among their taught“catalytically-active carbonaceous chars,” it is noted that thecatalytic activated carbon disclosed herein is distinguished from the'458 teaching and is distinctive in its surprising and unexpected (basedon the '458 teaching) properties for the removal of chloramine.

[0026] The catalytic activated carbon of the present invention isgenerally prepared by the method disclosed in U.S. Pat. No. 4,624,937,which disclosure is incorporated herein, by reference. The '937 patentteaches a method for catalytically oxidizing tertiary amines orsecondary amines in the presence of oxygen or an oxygen-containing gasto selectively produce secondary or primary amines, which methodcomprises the step of treating the carbon catalyst to remove oxides fromthe surface thereof. In a preferred embodiment of the '937 patentteaching, the surface oxides on the carbon are removed by pyrolyzing thecarbon material at a temperature in the range of about 800° C. to about1200° C. while simultaneously passing a gas stream of anoxygen-containing gas and NH3 through the carbon material in a ratio ofup to 90:10 for a time sufficient to remove surface oxides from thecarbon. More particularly, the '973 patent teaches the carbon treatmentgas stream to include a NH₃/oxygen-containing gas mixture from the groupconsisting of NH₃/CO₂, NH₃/O₂, NH₃/H₂O, and NH₃/NO_(x), and preferablythe NH₃/oxygen-containing gas mixture is NH₃/H₂O. A particular featureof the invention disclosed and claimed herein is the discovery that thetreatment gas does not necessarily require an oxygen-containing gas tostrip oxides from the surface of the activated carbon in order to obtaina highly active catalytic carbon product. In fact, in view of the priorart teaching of the requirement of said gas, it was surprising to findthat enhanced chloramine removal efficiency was achieved by treatmentwith ammonia alone. Furthermore, treatment of an activated carbon (suchas those obtained from coal, wood, nut shell, pitch, peat, fruit pit,cellulose, lignin, and agricultural waste materials) with ammonia in theabsence of an oxygen-containing gas, such as steam, resulted insignificantly higher product yields as a result of reduced carbonburn-off (gasification). This is a distinct economic benefit,particularly for high treatment temperatures (e.g., 950° C.) wherecarbon burn-off in the presence of steam reduced product yields to nearhalf that obtained in the absence of steam.

[0027] Using independent, outside test laboratories andindustry-accepted protocols, the invention catalytic activated carbonproduct was evaluated against Calgon Carbon's Centaur® catalyticcarbonaceous char product (taught in U.S. Pat. No. 5,338,458) for thereduction of chloramine in drinking water. The independent test dataindicated, and the applicants' findings support, that at chloramineconcentrations typical for drinking water the invention carbon has asubstantial performance advantage over Centaur with respect to bothvolumetric capacity and kinetics of eliminating chloramine from drinkingwater. Furthermore, contrary to the teaching of Calgon Carbon's '458patent, the applicants have demonstrated that high performance forremoval of chloramine can be obtained using carbons that exhibitrelatively low catalytic activity as determined by a surrogate “t-¾time” test. (In a variation of the t-¾ time test, considered to beequivalent to the t-¾ test procedure patented by Calgon Carbon (U.S.Pat. No. 5,470,748), instead of monitoring the rate of decomposition ofhydrogen peroxide in the presence of an activated carbon by measuringthe temperature of the hydrogen peroxide solution under essentiallyadiabatic conditions, the applicants measured the weight loss resultingfrom the evolution of oxygen during the carbon-catalyzed decompositionof the hydrogen peroxide under otherwise similar conditions of hydrogenperoxide concentration, carbon loading, and pH, etc. Reference to thissurrogate t-¾ test will be in quotation marks.)

[0028] In fact, the “t-¾ time” of some of the carbons that exhibited atleast twice the chloramine removal performance of Centaur was over 100minutes, well outside the broadest claim of the '458 patent (<15minutes).

Chloramine Reduction

[0029] Data obtained through the applicants' own experiments on theinvention catalytic activated carbons and related carbon productsconfirmed the superior performance of the invention catalytic activatedcarbon for removal of chloramine from water. The example below was theresults of tests run on the carbon products (≧90%-325 mesh) using aconcentration of chloramine near 3 ppm, a typical level for drinkingwater, at a temperature of 21° C. (70° F.). The chloramine solution wasprepared by blending one liter of a solution of ammonium chloride (1.500g NH₄Cl) in water with one liter of a solution containng sodiumcarbonate (1.250 g Na₂CO₃) and Chlorox household bleach (6% NaOCl, 12ml) in water. This stock solution, containing about 300 ppm ofchloramine (NH₂Cl), was equilibrated at 21° C. for one hour. A solutioncontaining about 3 ppm chloramine was prepared by diluting 10.0 ml ofthe stock solution to one liter with water. The actual concentration ofthe diluted chloramine solution was determined using the colorimetricprocedure described in Example 1 (with the omission of the carbon). Thistest solution of chloramine was equilibrated at 21° C. for one hourbefore use. All solutions were prepared on the day of the tests usinghigh purity water and, with the exception of the Chlorox bleach,analytical grade reagents.

[0030] For the purpose of characterizing the chloramine removalperformance of a given carbon product, it can be assumed that, under theconditions of preparation of the chloramine solutions, all the chlorinein the test solution is present in the form of monochloramine, NH₂Cl.The high ratio of NH₄Cl to NaOCl (5:1, compared to a stoichiometricratio of 1:1) used in the preparation of the solutions ensured that thereaction between the ammonium chloride and the sodium hypochlorite wouldbe driven rapidly towards the production of the monochloramine species.Furthermore, the pH of the test solution was about 8.3, a valueconsistent with the range in which “chlorine” is present in the solutionas the monochloramine species; i.e., not as “free chlorine” (HOCl orOCl⁻) or dichloramine (NHCl₂) or trichloramine (NCl₃). Supportingdocumentation in this respect can be found in, for example, the USEPAGuidance Manual “Alternative Disinfectants and Oxidants” (April 1999,pp. 6-1 to 6-35); in the Hach Company's Booklet Number 17, “CurrentTechnology of Chlorine Analysis for Water and Wastewater” by Daniel L.Harp (1995, pp. 1-30); and in the Hach Company's MonochloramineApplication Note reprinted from the article, “Specific Determination ofInorganic Monochloramine in Chlorinated Wastewaters” (Water EnvironmentResearch, 75(6), pp. 706-713).

EXAMPLE 1

[0031] 400 g of water containing chloramine (about 3 ppm) wasequilibrated at a temperature of 21° C. 200 mg (±1%) of the carbon testsample was added to the stirred solution and a stopwatch started torecord elapsed time. 10 ml aliquots of the carbon/water suspension wereremoved at periodic intervals and immediately filtered to remove thecarbon from treated water. The actual time of filtration of an aliquotof the carbon/water suspension was recorded as the elapsed time for thataliquot. The aqueous filtrates were analyzed for chloramine contentimmediately following collection of all aliquots of the carbon/watersuspension. Working with one filtrate at a time, a DPD(N,N-diethyl-p-phenylenediamine) reagent “pillow” for total chlorinedetermination (Hach Company, Catalog Number 21056-69) was added to thefiltrate (10 ml) and the sample vial shaken for 20 seconds to developthe characteristic magenta color of the “Wurster dye” DPD-oxidationproduct. The absorbance of the filtrate at a wavelength of 515 nm wasmeasured and the concentration of chloramine remaining in the water wascalculated using the appropriate calibration. A “blank” colorimetrymeasurement was made on the high purity water used to prepare thechloramine solutions to ensure that the absorbance at 515 nm was ±0.001.To compare data for different carbons, chloramine concentration datawere normalized to 200.0 mg of carbon on a dry weight basis.

[0032] Representative data are shown in FIG. 1 and Table I for a seriesof carbon products isolated from the production process described in the'937 patent under various conditions of ammonia and steam flows. Datafor the Centaur product are included for comparison. (Some of the datafrom Table I are graphically represented in FIG. 1.) TABLE I “t-¾ time”Chloramine Removed Carbon Sample (minutes) at 1 minute (%) C1 115 68 C26.8 81 C3 3.2 83 C4 330 50 C5 14.5 65 C6 4.3 75 Centaur 21 30

[0033] It is apparent from FIG. 1 and Table I that all the inventioncatalytic carbon products exhibited much faster kinetics of chloramineremoval from water than Centaur. For example, at an elapsed time of oneminute, the invention C3 product reduced the chloramine concentration by83% compared to only a 30% reduction for the Centaur product. Given thelow contact time in water-treatment filters, the kinetics of chloramineremoval are of considerable importance with respect to point-of-entry(POE) and point-of-use (POU) filters for residential use and commercialuse (e.g., restaurants, beverage manufacture).

EXAMPLE 2

[0034] The performance data discussed in Example 1 (FIG. 1 and Table I)were determined using equivalent weights of catalytic carbon products,namely 200 mg. However, POE and POU filters for water-treatmentapplications contain cartridges of certain standard dimensions, andtherefore accommodate a certain fixed volume of filtration medium.Depending on the nature of the precursor material from which a carbonproduct is produced, the density of different catalytic carbon productscan vary widely, resulting in different weights of the respectiveproducts in a fixed volume of a filter cartridge. For the case in point,the invention carbons were produced from wood, whereas the Centaurproduct was produced from coal. For comparable particle sizes, i.e.,≧90%-325 mesh, the apparent density of the coal-based Centaur product isabout twice that of the wood-based invention carbons. In practice, thismeans that a cartridge filter of a given volume can hold twice theweight of the Centaur product than of, in this example, a wood-basedcarbon.

[0035] If, for the purpose of illustration only, the Centaur andinvention carbons exhibited equal chloramine removal performances on agravimetric (weight) basis, it would be expected that the denser Centaurproduct would exhibit about twice the performance of the inventioncarbon on a volumetric basis. As the data in FIG. 1 and Table Idemonstrate, however, the gravimetric-based performance of the Centaurproduct falls far short of the invention carbons at contact times lessthan one minute. Nevertheless, tests were run on equivalent volumes ofthe Centaur product and invention carbons to further demonstrate thesuperior chloramine removal performance of the invention carbons. Thetests were run using the procedure described in Example 1, with theexception that the weight of Centaur used in the test was 400 mg,compared to 200 mg of the invention carbons. These weights correspondedto a volume loading of 1.71 ml of carbon per liter of test water.Representative data are shown in FIG. 2 for the Centaur product andinvention carbon C3. The chloramine removal performances are expressedin the volumetric-based units of g of chloramine removed per liter ofcarbon.

[0036] Clearly, the invention carbon still exhibited substantiallysuperior performance compared to the Centaur product, despite the factthat the Centaur product was present in the test water at twice theweight of the invention carbon. In fact, it is also clear from FIG. 2that the performance of the Centaur product at contact times below oneminute did not increase in proportion to the doubling of the weight ofCentaur product present in the test water. Because the removal ofchloramine from water is a result of the catalytic reduction of thechloramine by the carbon, it does not necessarily result that twice theweight of a given product doubles the rate of removal of chloramine fromthe water. The nature of the time-dependent curve in FIG. 2 for theCentaur product also reveals another reason why the performance of theCentaur product did not increase in proportion to the weight used.Namely, the “S-shaped” character of the curve at the low contact timesrelevant to practical use (in POE and POU filters) indicates that theCentaur product was slow to “wet” in the test water, which impeded itsability to catalyze the desired reaction. This is a featurecharacteristic of coal-based carbons, which tend to be more hydrophobicin nature than wood-based carbons.

Catalytic Activity

[0037] The catalytic activity of the catalyst plant products and Centuarwas measured using the surrogate “t-¾ time” test. The procedure andresults are set forth in Example 3.

EXAMPLE 3

[0038] The t-¾-time is defined (U.S. Pat. Nos. 5,338,458, 5,356,849, and5,470,748) as the time at which three-quarters (75%) of the maximumtemperature rise has occurred during the decomposition of hydrogenperoxide by a carbon material. It is assumed that this time correspondsto 75% decomposition of the available hydrogen peroxide. In thesurrogate “t-¾ time” test used to characterize the catalytic activity ofthe invention carbon products, the decomposition of the hydrogenperoxide solution was monitored through the weight loss resulting fromthe evolution of oxygen. In keeping with Calgon Carbon's definition, the“t-¾ time” was assumed to correspond to the point at which 75% of thetheoretical weight loss of oxygen from the available hydrogen peroxidehad occurred. The weight of carbon, volume of hydrogen peroxidesolution, and concentration of the hydrogen peroxide solution weresimilar to those employed in the Calgon Carbon test. Similarly, thereaction medium was buffered at pH 7.

[0039] The “t-¾ time” test data are summarized in Table I, above.Examples of the weight loss curves used to calculate the “t-¾ times” forthe invention carbon products are shown in FIG. 3.

[0040] It is clear from Table I that the invention carbon productsexhibited a wide range of “t-¾ times,” from 3.2 to 330 minutes, yet allexhibited high performance for removal of chloramine from water; i.e.,50-83% reduction, compared to only 30% for Centaur. More to the point,the “t-¾ times” of the C1 and C4 products, 115 and 330 minutes,respectively, were substantially greater than the primary claim in the'458 (chloramine use) patent, which is limited to carbon productsexhibiting t-¾ times of less than 15 minutes, which would suggest to oneskilled in the art that the invention carbon products C1 and C4 areunsuitable for chloramine removal as compared to thecatalytically-active carbonaceous chars of the '458 patent.

[0041] The large difference between the catalytic activities of the C1and C4 invention carbons and the prior art Centaur product is furtherexemplified in FIG. 3, where the weight loss due to the evolution ofoxygen during the decomposition of the hydrogen peroxide solution isshown as a function of time. The two lower curves for the C1 and C4products reflect their relatively low activity towards hydrogen peroxidedecomposition compared to the Centaur product. Despite this, the C4 andC1 products exhibited 170-230% of the performance of the Centaur productfor removal of chloramine (50 and 70%, respectively, compared to 30% forCentaur). Conversely, the C3, C6, and C2 products in Table I exhibitedfast “t-¾ times,” 3.2, 4.3, and 6.8 minutes, respectively, but theperformance gains in removal of chloramine were modest relative to theC1 product. Yet, all sample invention activated carbon productsexhibited far superior abilities for removal of chloramine over the '458patent product.

[0042] Inasmuch as the surrogate “t-¾ time” test is essentiallyequivalent to the t-3/4 time test of the '458 patent, it appears fromthe data presented that the time measure of the decomposition of 75% ofthe theoretical weight loss of oxygen from the available hydrogenperoxide had occurred in the presence of a given amount of carbon is notan accurate indication of that carbon's ability to remove chloraminefrom drinking water. This is exemplified in graphical form in FIG. 4,which demonstrates that there is a very poor correlation between “t-¾time” and the chloramine reduction performance of catalytic carbons(i.e., very low regression coefficient, “R²,” of 0.155). The applicantshave shown that carbons with “t-¾ times” well beyond the time taught inthe '458 patent to be extremely poor candidates for removing chloramine,in fact, are much better candidates than those taught as excellentcandidates in said patent disclosure. The conflict between the datapresented herein and the faulty teaching of the '458 patent begs thequestion, “What carbon material characteristic (or characteristics),then, will provide an accurate indication for enhanced removal ofchloramine?”

[0043] The applicants sought to understand the reasons for the differentchloramines removal efficiencies between the similarly treated prior artCentaur® product and the invention activated catalytic carbon. It wasdetermined, therefore, to analyze both materials to explore whether sucha result involves differing ways the nitrogen enhancement of the carbonoccurs. Certainly, the data shown graphically in FIG. 5 indicate thatthere is a good correlation between the increase in nitrogen content andthe improved catalytic activity of carbon products with respect tochloramine reduction in water (i.e., a relatively high regressioncoefficient, “R²,” of 0.953).

EXAMPLE 4

[0044] In photoelectron spectroscopy (XPS) analysis, a sample of amaterial is bombarded with X-ray radiation, causing photoelectrons to beemitted from a core atomic level of the material. Depending on theenergy of the atomic level, and of the incident X-ray radiation, theemitted photoelectron has a defining binding energy, enabling elementaland complex chemical state identifications to be made.

[0045] The XPS data are summarized in Table II, in which the inventioncarbons are identified as “C7” through “C13.” The prior art catalyticactivated carbon of the '937 patent is identified as “P1,” and the priorart Centaur product of the '458 patent is identified as “P2.” XPS peaksfor nitrogen electrons (Is atomic level) were observed at bindingenergies of 398-398.4, 399.5-400.6, 401.1, and 403.5 electron volts(eV), respectively. XPS peaks at these binding energies are associatedwith pyridine (acridine), aromatic (“center”), aromatic (“valley”), andammonium ion nitrogen species, respectively [1. Pels, J. R., Kapteijn,F., Moulijn, J. A., Zhu, Q., and Thomas, K. M., “Evolution of NitrogenFunctionalities in Carbonaceous Materials During Pyrolysis,” CARBON,(1995), 33(11), pp. 1641-1653; 2. Bradley, R. H., Hellebust, S., andDaley, R., “On the Chemistry of Nitrogen in the Graphene Structure,”Extended Abstracts of the 24^(th) Biennial Conference on Carbon,Charleston, S.C., Jul. 11-16, 1999, pp. 420-421]. For purpose ofclarification, these nitrogen species are represented by (a), (b), (c),and (e), respectively, in FIG. 6. XPS peaks at binding energies of 400.5and 401.1 electron volts can also be associated with primary aminogroups, represented by (d) in FIG. 6. However, primary amino groups arerelatively unstable, and their XPS signatures disappear upon thermaltreatment of carbon at temperatures >400° C. [Cuesta, A.,Martinez-Alonso, A., Tascon, J. M. D., and Bradley, R. H., “ChemicalTransformations Resulting from the Pyrolysis and CO₂ Activation ofKevlar Flocks,” CARBON, (1997), 35(7), pp. 967-976]. Both the inventionand prior art carbons had been exposed to temperatures considerablyhigher than 400° C. during their processes of manufacture, and thereforethe presence of amino species in the carbons is considered unlikely.

[0046] The XPS data in Table II reveal that that the nitrogen surfacechemistries of the invention carbons C₇-C₁₃ and the P1 prior art carbonwere very different from that of the prior art Centaur product (P2). TheC₇-C₁₃ and P1 carbons, all of which were produced by contacting anactivated carbon with ammonia at a high temperature in the range of780-960° C., exhibited a significant amount of nitrogen that was presentas an aromatic, center species {(b) in FIG. 6}. It is also clear fromTable II that, in general, as the proportion of this nitrogen speciesincreased in the carbon product as a result of more favorable processconditions, notably increased temperature of treatment, the chloraminereduction performance of the carbon was enhanced, particularly withrespect to the kinetics of chloramine reduction. In very markedcontrast, no evidence was found for the presence of the same nitrogenspecies in the prior art Centaur product (P1). In this context, it isstriking that the chloramine reduction performance of the prior artCentaur product was poor. TABLE II Process Conditions CatalyticProperties Gas NH₂Cl Nitrogen Content Carbon Reactants “t¾ ReductionAromatic Sample Carbon Temp Present time” 1-min¹ 60%² Total N “Center”Number Precursor (° C.) NH₃ Steam (min) (%) (min) (wt %) (%)³ (wt %) C7Wood 788 Yes Yes >4300 40 2.3 3.4 46 1.57 C8 788 Yes No 3000 67 0.8 2.375 1.75 P1 843 Yes Yes 6.0 83 0.6 2.5 46 1.14 C9 899 Yes Yes 1.8 95 0.44.8 70 3.39 C10 899 Yes No 6.5 91 0.3 3.0 66 1.98 P2 Prior Centaur AsReceived 21 30 1.8 1.3 0 0 C11 Art 788 Yes Yes 10 77 0.4 3.0 73 2.17 C12Centaur 788 Yes No 7.2 80 0.5 1.8 78 1.43 C13 Product 954 Yes No 2.0 900.3 2.5 86 2.17

EXAMPLE 5

[0047] Of even greater significance, however, is the fact that when theprior art Centaur product itself was similarly treated with ammonia, thechloramine reduction performance of the product obtained was comparableto the high levels of the invention carbons C₈-C₁₀ and the prior artcarbon P1. This is clearly evident from the data shown in Table II forthe invention carbons C11-C13; namely those produced by treatment of theprior art Centaur product (P2) itself according to the inventionprocess. It is equally clear that whereas no aromatic, centerconfiguration nitrogen was detected in the prior art Centaur productitself, the subsequent treatment of the Centaur product introducedsubstantial levels of the same nitrogen species {(b) in FIG. 6}. Infact, as the total nitrogen content of the Centaur-based carbon wassubstantially enhanced through application of the invention process, theproportion of the aromatic, center nitrogen species in the productobtained was as high as almost 90% of the total nitrogen content of theproduct, resulting in a dramatic improvement in the chloramine reductionperformance of the treated Centaur product. This is shown graphically inFIG. 7.

[0048] These findings are unexpected given that both the invention andprior processes for manufacture of the respective carbon productsinvolve high temperature treatment of carbons, activated or otherwise,with nitrogen-containing materials. Yet, the invention process resultsin a carbon product that contains a far greater amount ofcatalytically-active nitrogen species, both in absolute and relativeterms, which greatly contribute to the much superior performance of theinvention carbon for chloramine reduction in water. In fact, the priorart Centaur process ('458 patent) did not significantly enhance thetotal nitrogen content of the carbon product over that of the“nitrogen-poor” char or activated carbon precursor material used in theprocess. For example, coal-based carbon used in the prior art processtypically contains about 0.9 wt % total nitrogen content; i.e., beforethermal treatment with a nitrogen-containing material such as urea. Asthe data in Table II show, the total nitrogen content of the prior artCentaur product (P2) was 1.3 wt %; i.e., an increase (difference) of 0.4wt % over that of a coal-based precursor carbon. Furthermore, it wasrevealed through XPS analysis that the bulk (65%) of the 0.4 wt %increase in total nitrogen content of the product was found to beassociated with ammonium ion {(e) in FIG. 6}; i.e., an ammonium saltby-product from the urea treatment that is unlikely to be catalyticallyactive for chloramine reduction in water. In essence, therefore, theactual increase in the amount of a catalytically-active nitrogen speciesin a carbon treated according to the prior art process ('458 patent) wasextremely small, which is entirely consistent with the poor performanceof the prior art Centaur product for chloramine reduction in water.

EXAMPLE 6

[0049] Overall, the data shown in Table II indicate that the performanceof a catalytic activated carbon for chloramine reduction in water can becorrelated with a specific nitrogen chemical species. Namely, aromaticnitrogen, and more specifically, the center configuration of aromaticnitrogen in a graphene layer {(b) in FIG. 6}. In general, as theproportion of this nitrogen species increased in the carbon product as aresult of more favorable process conditions, the chloramine reductionperformance of the carbon was enhanced. A notable example of this isprovided by the two invention carbons, C7 and C8. These were obtained bytreatment of a wood-based activated carbon with ammonia at 788° C. inthe presence (C7) and absence (C8), respectively, of steam. Despite thefact that the ammonia-only treatment (C8 carbon) resulted in a lowertotal nitrogen content (2.3 wt %) compared to the conventionalammonia/steam treatment (C7 carbon, 3.4 wt %) described in theapplicants' pending application Ser. No. 10/141,158, filed May 8, 2002,the chloramine reduction performance of the C8 carbon was substantiallygreater than that of the C7 carbon (FIG. 8). This finding is consistentwith the fact that the ammonia-only treatment (C8 carbon) resulted in agreater proportion and absolute amount of the aromatic, center nitrogenthat is believed to be the predominant nitrogen species associated withcatalytic activity for chloramine reduction in water. It is alsonoteworthy that the C7 and C8 carbons exhibited extremely long “t-¾times” (>4300 and 3000 minutes, respectively), further emphasizing thefact that there is no meaningful relationship between t-¾ time, asdetermined through the hydrogen peroxide test of the '458 patent, andthe chloramine reduction performance of a catalytic activated carbonproduct. In fact, on the basis of the teaching of the '458 patent,neither of the C7 and C8 invention carbons should have exhibited anysignificant activity for chloramine reduction in water, let alone thefairly good performance of the C8 invention product.

[0050] A similar finding was obtained for the corresponding inventioncarbons (C11 and C12) produced from the treatment of the prior artCentaur product (P2) with ammonia in the presence (C11) and absence(C12) of steam, respectively, at 788° C. In this instance, the relativeincreases in chloramine reduction performance and proportion of aromaticnitrogen species were much smaller because the chloramine reductionperformance of the C11 carbon obtained from the treatment of the priorart Centaur product with both ammonia and steam was much higher thanthat of the corresponding C7 carbon; namely, one-minute chloraminereduction figures of 77 and 40% respectively. Based on the prior artteaching, this was an unexpected finding that a coal-based carbon, whensubjected to the treatment of the invention process, would more readilyyield a product exhibiting high catalytic activity for chloraminereduction than a wood-based carbon under otherwise comparable processingconditions.

Solid Carbon Block

[0051] For various reasons, the water filter industry favors carbonblocks for POE and POU filters. Primarily, in such form they are easy tohandle and exhibit lower dust levels. Both of these facts are moreconducive to filter change-outs by the consumer. In the manufacture ofthe carbon blocks, the carbon is blended with a suitable binder,typically high-density polyethylene, and the carbon block formed thougha number of distinct, proprietary processes.

EXAMPLE 7

[0052] In a laboratory test, an invention carbon product 50×200 meshparticle size) was melt-blended with high-density polyethylene (HDPE)powder at a level of 20% of the dry carbon weight (1 part binder to 5parts carbon). The solid block formed from the carbon and HDPE binderwas crushed and screened to give material that was >90%-325 meshparticle size. The Centaur prior art carbon product was similarlymelt-blended with HDPE, and the resulting block crushed to −325 meshparticle size. Using a 3 ppm chloramine solution in water, thechloramine reduction performance of each of the powdered, HDPE-treatedcarbons was determined in a manner similar to that described inExample 1. The amount of sample in each test corresponded to 200 mg ofcarbon (dry basis). The data obtained are summarized in Table III,together with the corresponding data for the original carbons (nottreated with HDPE). The data are also shown graphically in FIG. 9 topermit a more ready comparison. TABLE III Influence of HDPE Binder onChloramine Removal Performance of Catalytic Carbons Amount of ChloramineRemoved (%) Invention Prior Art Carbon Carbon (Centaur) Contact TimeWithout With Without With (minutes) Binder Binder Binder Binder 2 83 453 87 26 5 100 100 82 42 10 100 100 100 60 15 100 100 100 69

[0053] It is apparent from FIG. 9 and Table III that melt-blending theinvention carbon with HDPE binder did not impact the chloraminereduction performance of the invention carbon. In a time frame relevantto POU filters, chloramine in the test water was quickly reduced by boththe original prior art carbon and the HDPE-treated prior art carbon. Inmarked contrast, however, it is equally apparent from FIG. 9 that theHDPE binder had a pronounced, adverse impact on the chloramine reductionperformance of the prior art Centaur® product. The performance of theprior art carbon product was reduced by over 50% following melt-blendingwith the HDPE binder at the 20 wt % level typically used for filterblock manufacture. This substantial loss in chloramine reductionperformance of the prior art carbon was attributed to, as mentionedearlier, the poor wetability of the Centaur® product, which isexacerbated upon addition of a hydrophobic binder such as polyethylene.In fact, although the same test protocol was used for both the inventionand prior art carbon products, it was necessary to add a small amount ofsurfactant to the water containing the prior art carbon to get thecarbon to wet at all. In the absence of the surfactant, the HDPE-treatedprior art carbon did not wet over the fifteen-minute time frame of thetest, resulting in little measurable chloramine reduction in the testwater. In marked contrast, the invention carbon product readily wettedin both the virgin and blended forms, did not require a surfactant, andexhibited substantially superior chloramine removal performance.

[0054] In summary, the invention carbon could be formed into blocks,using a standard polyethylene binder, without loss of chloraminereduction capacity.

[0055] While presently preferred embodiments of the invention have beendescribed in detail, the invention may be otherwise embodied within thescope of the appended claims.

What is claimed is:
 1. A process for the removal of chloramines fromchloramine-containing fluid solutions or streams comprising the step ofcontacting said solutions or streams with an activated carboncharacterized by having present in the graphene structure of the carbonfrom 0.01 to 10 wt % of aromatic nitrogen species.
 2. The process ofclaim 1 wherein the carbon has been treated by a process of pyrolyzingthe carbon while simultaneously passing a gas stream containing NH3through a bed of the carbon.
 3. The process of claim 1 wherein at least10% of the nitrogen is positioned as an aromatic center configurationwithin a graphene layer.
 4. The process of claim 2 wherein the gasstream includes both NH3 and an oxygen-containing gas or vapor.
 5. Theprocess of claim 4 wherein the gas stream includes aNH₃/oxygen-containing gas mixture from the group consisting of NH₃/CO₂,NH₃/O₂, NH₃/H₂O, and NH₃/NOX.
 6. The process of claim 5 wherein theNH₃/oxygen-containing gas mixture is NH₃/H₂O.
 7. The process of claim 1wherein the solutions or streams are aqueous.
 8. The process of claim 1wherein the activated carbon is derived from a carbon-containingmaterial.
 9. The process of claim 8 where the carbon-containing materialcontains nitrogen in its chemical structure.
 10. The process of claim 8wherein the activated carbon is derived from a material selected fromcoal, wood, nut shell, pitch, peat, fruit pit, cellulose, lignin, andagricultural waste materials.
 11. The process of claim 1 wherein thepyrolyzing temperature is above about 700° C.
 12. The process of claim 1where the carbon is shaped in the form of a block.
 13. The process ofclaim 3 where the carbon is shaped in the form of a block.
 14. Theprocess of claim 9 where the carbon is shaped in the form of a block.15. The process of claim 1 wherein the carbon is characterized by thepresence in the graphene structure of the carbon of from 0.02 to 7 wt %of aromatic nitrogen species.
 16. The process of claim 15 wherein thecarbon is characterized by the presence in the graphene structure of thecarbon of from 0.03 to 5 wt % of aromatic nitrogen species.
 17. Anactivated carbon useful for the removal of chloramines fromchloramine-containing fluid solutions or streams wherein the carbon ischaracterized by the presence in the graphene structure of the carbon offrom 0.01 to 10 wt % of aromatic nitrogen species.
 18. The carbon ofclaim 17 wherein the solutions or streams are aqueous.
 19. The carbon ofclaim 17 wherein the activated carbon is derived from acarbon-containing material.
 20. The carbon of claim 19 wherein theactivated carbon is derived from a material selected from coal, wood,nut shell, pitch, peat, fruit pit, cellulose, lignin, and agriculturalwaste materials.
 21. The carbon of claim 17 wherein at least 10% of thenitrogen is positioned as an aromatic center configuration within agraphene layer.
 22. The carbon of claim 17 wherein the carbon has beentreated by a process of pyrolyzing the carbon while simultaneouslypassing a gas stream containing NH3 through a bed of the carbon.
 23. Thecarbon of claim 22 wherein the gas stream includes both NH3 and anoxygen-containing gas or vapor.
 24. The carbon of claim 23 wherein thegas stream includes a NH₃/oxygen-containing gas mixture from the groupconsisting of NH₃/CO₂, NH₃/O₂, NH₃/H₂O, and NH₃/NO_(x).
 25. The carbonof claim 24 wherein the NH₃/oxygen-containing gas mixture is NH₃/H₂O.26. The carbon of claim 23 wherein the pyrolyzing temperature is aboveabout 700° C.
 27. The carbon of claim 17 wherein the carbon ischaracterized by the presence in the graphene structure of the carbon offrom 0.02 to 7 wt % of aromatic nitrogen species.
 28. The carbon ofclaim 27 wherein the carbon is characterized by the presence in thegraphene structure of the carbon of from 0.03 to 5 wt % of aromaticnitrogen species.
 29. The carbon of claim 19 wherein thecarbon-containing material is in the form of a single compoundcomprising nitrogen in its chemical structure.
 30. The carbon of claim21 wherein the carbon is shaped in the form of a block.
 31. The carbonof claim 27 wherein the carbon is shaped in the form of a block.
 32. Thecarbon of claim 28 wherein the carbon is shaped in the form of a block.